The present invention relates to a method for identifying a position of an automated guided movable body such as an automated guided vehicle on a field inside or outside of a factory, and to an apparatus of detecting a position of a movable body to be used in carrying out the method.
An automated guided vehicle is often used for transporting goods in a factory. In order to control travelling of the automated guided vehicle, it is necessary to identify the position and the travelling direction of the automated guided vehicle by means of a position detecting apparatus.
A movable body position detecting method and apparatus for identifying the position and the travelling direction of a movable body is disclosed, for example, in Japanese Patent Application Laid-open No. 09-105628/1997.
FIG. 1 is a block diagram showing a construction of the movable body position detecting apparatus disclosed in Japanese Patent Application laid-open No. 09-105628/1997. FIG. 2 is a perspective view showing an overall construction of the apparatus. The movable body position detecting apparatus includes a recognizing and identifying circuit 20 provided with a recognizing means 211 and a position calculating means 24, and an optical unit 10 disposed before the recognizing and identifying circuit 20. The position of a truck 30, which is a movable body, is detected by detecting the reflectors Hi by the optical unit 10 and analyzing the detection results by the recognizing and identifying circuit 20.
Three or more reflectors Hi are mounted on wall surfaces of a travelling area of the movable body. The reflectors Hi are formed by separately painted reflecting portions and non-reflecting portions so as to provide respective specific barcode-like marks formed by the reflecting portions and the non-reflecting portions arranged as horizontal bars with intervals and thicknesses different from each other.
FIG. 3 is an enlarged vertical cross-sectional view showing a construction of an essential part of the optical unit 10. The optical unit 10 is mounted on the truck 30 via a frame 31, and includes a laser oscillator 11 for outputting a laser light, an image sensor 121 for receiving the laser light reflected from the outside, a horizontally rotating turn table 131 for mounting these elements, and other elements. A tubular polygon mirror 17 having a regular polygonal shape in its vertical cross section and formed by a combination of a plurality of mirror plates 17c is mounted in front of the laser oscillator 11 so as to be vertically rotatable. A cover 131c for cutting off the outside light is mounted on the upper surface of the turn table 131, and an aperture 131c1 is disposed in a side surface of the cover 131c for irradiating and receiving the laser light.
The laser light irradiated from the laser oscillator 11 and reflected by the polygon mirror 17 travels through a half mirror 17b and is reflected by a tilted mirror 17a to exit through the aperture 131c to the outside. The laser light is reflected by the reflector Hi and passes through the aperture 131c1 to be reflected by the tilted mirror 17a and the half mirror 17b to be incident into the image sensor 121.
Since the polygon mirror 17 is rotating, the laser light exiting through the aperture 131c1 moves downwards by a predetermined distance while the laser light is hitting one mirror plate 17c. Further, since the optical unit 10 is rotated by means of the turn table 131, the laser light is also rotated to irradiate surroundings of the truck 30.
The laser light is reflected only when the laser light passes the reflector Hi, and the reflected light is incident into the image sensor 121. Also, since the irradiation of the laser light changes downwards, the reflector Hi is scanned over its entire width in the vertical direction. The data of the pattern of the scanned reflector Hi are input from the image sensor 121 to the recognizing means 211. The reflector Hi is identified by making reference to the data of the patterns previously stored in a storage means 221, and its coordinate values are obtained. In addition, an output at the scanning time from an encoder 15 mounted on a rotating shaft of the turn table 131 is input into an angle calculating means 25 to calculate an angle .theta.i of the direction of the reflector Hi relative to a reference direction.
Hereafter, a procedure for identifying the position of the movable body will be explained. FIG. 4 is an explanatory view showing positional relationship between the movable body and the scanned three reflectors. FIG. 5 is an explanatory view showing a procedure for identifying the position according to the prior art. Three or more reflectors Hi are scanned in the above-mentioned manner to determine their coordinate values Ai and their angles .theta.i relative to the reference direction. From the coordinate values Ai of the scanned reflectors Hi, three points A1, A3, A5 are selected, and the two points A1, A3 and the two points A3, A5 are respectively connected with a line. Here, the three points A1, A3, A5 are selected so that the angle .theta.k at each point satisfies 0.degree.&lt;.theta.k&lt;180.degree.. Two circles E1a, E1b and two circles E2a, E2b are determined having the lines as their chords and having the angle .theta.a between A1 and A3 and the angle .theta.b between A3 and A5 as their angles of circumference.
The intersecting points of the circles E1a, E1b, E2a, E2b are determined, and four points P1, P2, P3, P4 other than A1, A3, A5 are determined. The position of the truck 30 can be identified as one of the intersecting points P1, P2, P3, P4. For example, in order that the intersecting point P1 of the circles E1a, E2a is appropriate as representing the position of the truck 30, the intersecting point P1 must satisfy the following conditions simultaneously.
1. The coordinates of the intersecting point P1 lie within an area that the truck 30 can travel.
2. The intersecting point P1 lies on the same side as the center T1a of the circle E1a relative to the line segment connecting the points A1, A3 if the angle .theta.a&lt;90.degree., and lies on the different side from the center T1a relative to the line segment connecting the points A1, A3 if the angle .theta.a&gt;90.degree..
3. The intersecting point P1 lies on the same side as the center T2a of the circle E2a relative to the line segment connecting the points A3, A5 if the angle .theta.b&lt;90.degree., and lies on the different side from the center T2a relative to the line segment connecting the points A3, A5 if the angle .theta.b&gt;90.degree..
4. The points A1, A3, A5 are arranged clockwise in this order from the reference direction with the intersecting point P1 being the center when scanned clockwise.
Here, the conditions 2, 3 are based on the fact that the intersecting point P1 is an intersecting point of the circles E1a, E2a. Therefore, the one point appropriate as the position of the truck 30 can be identified by observing the fact that the intersecting point P2 is the intersecting point of the circles E1b, E2b, the intersecting point P3 is the intersecting point of the circles E1b, E2a, and the intersecting point P4 is the intersecting point of the circles E1a, E2b, and examining whether similar conditions are satisfied at each intersecting point. Also, the direction of the truck 30 can be determined on the basis of the angle .theta.1 of the coordinates A1 relative to the reference direction N as viewed from the intersecting point P1 thus identified.
In the meantime, according to the conventional movable body position detecting method and apparatus as described above, the position of the movable body is identified based on triangulation, so that it is necessary to determine which of the reflectors numerously disposed in the moving area the detected reflector is. For this reason, it is necessary that each reflector includes a mark such as a barcode specific to the each reflector, the reflector is scanned by scanning the wall surfaces both horizontal rotating direction and vertically by means of the laser light, and each reflector is identified by means of the read mark.
Further, since the wall surface is scanned sequentially in the rotating direction of the turn table, a time difference occurs in detecting the plurality of reflectors. Since the movable body is moving during a period of time between detection of one reflector and detection of the next reflector, the detecting error will become larger if the position of the truck is detected by using this detection result. Also, the process will be complex ir the position of the truck is calculated by taking the moving distance of the movable body into consideration in order to avoid this detecting error.
Moreover, since the apparatus includes a rotating mechanism for a turn table, the apparatus is large in size and the costs of the electric power supply and others are high.
Further, the detecting error becomes larger due to the looseness caused by backlash sliding abrasion of the rotating section or the like.
Also, if the detecting apparatus is used in a clean room, it will be a source of dust generation due to the sliding movement of the movable parts.